openssh: Fix non-deterministic build behaviour

If maillock.h is found, a dependency on liblockfile will be created.
liblockfile is in meta-oe, so we don't want that in an oe-core recipe.

Signed-off-by: Dan McGregor <dan.mcgregor@usask.ca>
Signed-off-by: Ross Burton <ross.burton@intel.com>